A Case-Control Study of diabetic retinopathy is underway comparing age and duration matched long term insulin dependent diabetics with and without retinopathy in regard to certain demographic, ocular, systemic, and metabolic factors to see if a profile for the high risk of retinopathy patient can be developed. Patients with little or no retinopathy will be followed prospectively to assess the predictive value of the factors identified. A detailed manual of procedures (MOP) has been developed, forms and procedures tested, and patient recruitment has begun. We hope to follow-up on several cohorts of patients previously seen at the Joslin as part of the screening for case control patients. Among the factors being studied will be diabetic onset symptoms, blood sugar levels, cigarette smoking, Hemoglobin A1C, growth hormone and glucagon after arginine stimulation, sedimentation rate, lipid profile including HDL cholesterol, 2'3 DPG, platelet aggregation, platelet growth factor, intraocular pressure, refractive error, lens autofluorescence. Vitreous fluorophotometry and mean retinal circulation time measurements using computer densitometric reading of fluorescein angiograms will be done on selected patients.